Topographic variations of soil properties and stand structure in a Pinus thunbergii plantation

Abstract

Soil properties and above-and belowground forest structure were studied across various topographies in a 20-year-old Pinus thunbergii Parl. plantation on Mt Tanakami, Japan. The soil properties and stand structure varied greatly with slope position from ridge top to valley floor. Soil thickness, fine soil content and soil moisture content were greater in lower slope positions. The amount of organic carbon in the forest floor was greater in upper slope positions. The organic carbon content in the mineral soil was slightly greater in lower slope positions. These changes in soil properties suggested an upslope decrease in decomposition rate and water and/or nutrient availability. The aboveground structure of P. thunbergii was more developed at lower slope positions. The mean stem diameter, height and volume of P. thunbergii increased downslope with decreasing tree density. However, fine root biomass increased greatly upslope. This inverse relationship between tree height and fine root biomass indicated morphological plasticity of P. thunbergii in exploiting environmental heterogeneity. Variations in soil-plant interactions in the stand along various topographies caused spatial heterogeneity in the accumulation pattern of organic matter in plants and the soil.

Characteristics of soil respiration in upper and lower slope positions with different aboveground biomass: a case study in a Japanese cypress forest

“…SWC was significantly lower in the UP than in the LP. Lower SWC was also observed in upper slope in previous studies Enoki et al, 1996;Tamai 2010 . Generally, the soil water content decreases upslope because of hydrological processes.…”

“…The multiple linear regression results showed that fine root biomass accounted for the additional spatial variation in R soil that was not explained by SWC and T soil , because AIC and R 2 of the best-fit model including fine rot biomass as an explanatory factor was better for other models without fine root biomass. Fine root biomass often determines the heterogeneity in R soil Katayama et al, 2009;Shibistova et al, 2002 , and fine root biomass often differs with slope position Enoki et al, 1996;Tateno et al, 2004 . Thus, fine root biomass played an important role in understanding the heterogeneity in R soil on a slope.…”

“…For example, it has been shown that the nitrogen availability decreases upslope, and the aboveground biomass decreases and fine root biomass increases upslope, owing to a shift in carbon allocation from aboveground to belowground sources Enoki et al, 1996;Tateno et al, 2004 . High fine root biomass often facilitates root respiration and dead root decomposition, resulting in high R soil Katayama et al, 2009;Shibistova et al, 2002 .…”

Stem productivity in relation to nitrogen concentration and carbon isotopic composition (δ13C) in leaves of hinoki cypress (Chamaecyparis obtusa Endlicher) plantations in Shikoku district, Japan

“…2). Previous studies showed that the soil C/N ratio decreased from the upper to lower slope (Enoki et al 1996;Tateno and Takeda 2003) and a higher soil C/N ratio was found on the ridge (Enoki et al 1996). The high soil C/N ratio in the OKU6 indicates the soil condition of the site is dry enough even at the lower altitude, indicating that the shape of the relief, i.e., concave or convex, was more important than the altitude along the slope.…”

“…Previous studies have shown that stem productivity or height growth (site index) in Japanese forests is related to topography (Enoki et al 1996;Tateno and Takeda 2003;Zushi 2006) and soil type (Inoue et al 1973;Mashimo 1960). These studies suggest that soil water and nitrogen availability are the primary factors that determine stem productivity.…”